1. Field of the Invention
The present invention relates to a printing apparatus using a print ribbon, and more particularly to a printing apparatus wherein printing is effected with a print head moved in pressed contact with a print ribbon.
2. Discussion of the Prior Art
An example of a printing apparatus of the type indicated above is a typewriter equipped with a thermal printer which uses a print head adapted to print utilizing heat. The print head is movable between a printing position in which the print head is in pressed contact with a recording medium via a print ribbon, and a non-printing or release position in which the print head is spaced apart from the recording medium. Usually, the print head is mounted on a carriage or similar carrier, so that printing is effected while the print head is moved with the carrier along a line of printing.
The printing apparatus described above is commonly arranged such that an active portion of the print ribbon is supplied from a ribbon supply section (such as a supply spool of a ribbon cassette) and is fed past the print head. The used portion of the print ribbon which has passed the print head is moved into a ribbon take-up section (such as a take-up spool of the cassette) by suitable ribbon feeding means such as a ribbon take-up device. Thus, the print head is always loaded with an unused portion of the print ribbon.
The ribbon feeding means is operable while the print head is placed in its printing position. In this condition, the print ribbon is fed by a distance corresponding to a distance of movement of the print head. While the print head is placed in the release position, however, the ribbon feeding means is not operable. For example, the print head is moved to the release position when a carriage return takes place, with the print head returned to the beginning of a new print line, so that the print ribbon is not fed during a non-printing return movement of the print head.
Generally, the print head may be fed without a printing action, when a space key or other space commanding member is operated. When such a space commanding member is momentarily operated, the print head is fed by a distance equal to the selected printing pitch. Some printing apparatus have a so-called self-repeat spacing function wherein the print head is fed continuously by a distance equal to a multiple of the printing pitch, if the space commanding member is continuously operated or held in its operated position for a desired length of time corresponding to a desired distance of spacing.
In a conventional printing apparatus, the print head is moved to provide a spacing while the print head remains in its printing position, if a space commanding member is momentarily or continuously operated when the print head is in the printing position.
In the above arrangement wherein a spacing movement of the print head is effected while the print head remains in the printing position (in pressed contact with the print ribbon), the movement of the print head activates the ribbon feeding means to feed the print ribbon, and therefore causes waste of an unused length of the ribbon. To avoid this inconvenience, there has been proposed a technique to bring the print head to its release position prior to effecting a spacing movement of the print head.
However, the proposed arrangement causes another problem. That is, required overall printing time for a specific print job is increased due to extra non-printing time that must be spent in moving the print head to the release position and returning the same to the printing position each time a space is provided between successive English words, for example.
It has been also proposed to bring the print head to the release position by a suitable head release mechanism if a space key is operated two or more times. In this case, the print head is not moved to the release position when the space key is operated once to provide a single space. Consequently, the foregoing proposal is free from the above problem of extra non-printing time due to the movements of the print head between the printing and release positions. However, if the space key is operated two times to provide two spaces between sentences, the above problem is encountered. The problem is becoming more and more important, due to the recent tendency in thermal printer technology of using a motor as a drive source for the head release mechanism, in place of a conventionally used solenoid, in an attempt to reduce operating noises of the head release mechanism for moving the print head between the printing and release positions. Namely, the head release mechanism driven by a motor requires a longer operating time than the conventional solenoid-operated mechanism.